1. Field of the Invention
The present invention relates to a multi-purpose writing device which comprises a casing and plural writing elements contained in the casing, at least one of said writing elements being an automatic pencil that can be extended out of the casing.
2. Description of the Prior Art
Multi-purpose writing devices which respectively comprise a casing containing an automatic pencil and a ballpoint pen that can be extended out of the casing are know in the art. For example, there is known a writing device which comprises a guide cylinder containing an automatic pencil and a ballpoint pen in such a manner as to be axially slidable in directions different by 180.degree. from each other. A cylindrical cam is provided around the guide cylinder in a circumferentially movable manner for a given angle and is adapted to cause the writing elements to extend and retract alternately along the axis by engaging with the writing elements and further is movable in the axial direction to extend the automatic pencil out.
Multi-purpose writing devices in which plural writing elements are alternately extended and retracted between a writing position and a housed position by means of such a cam mechanism are proposed, for example, in Japanese Patent Publication Nos. Sho 57-50199 and Sho 55-38280.
In a prior art multi-purpose writing device in which the writing elements are extended to and retracted from the writing position by the reciprocal rotational movement of the cylindrical cam and pressing the automatic pencil out, the slide projection of the slider of either the pencil or ballpoint slides and projects on the cam surface and engages with the tip of the cam surface to extend one of the writing elements out from an opening at the tip of the casing. Thus, when the automatic pencil element is pushed, the slider thereof is pressed by the tip of the cam surface and the lead of the pencil is discharged.
Writing devices using the prior art cam mechanism had the following defects. In order to reduce the diameter of a cap, it is necessary to mold the cylindrical cam with a reduced thickness. The cam surface has, however, a very narrow angled tip. When the cylindrical cam and the slider are molded of metal, they can be operated relatively stably. On the other had, if synthetic resin is used for molding these parts, the cylindrical cam becomes deformed when rotated and causes the slide projection of the slider to be displaced from the cam surface and caught in the cam, thereby preventing smooth movement of the cam.
Positioning of the writing elements also tends to become unstable as it is determined only by the engagement of the cam at its tip with the slide projection of the slider.
Moreover, cylindrical cams made of synthetic resin are easily worn, especially at the tip of the cam surface, making it difficult to achieve complete engagement with the slide projection of the slider at a predetermined position. As a result, alternate movements of the writing elements to and from the writing position become unstable and insecure. Discharging the lead of the automatic pencil also becomes difficult.